1. Field of the Invention
The present invention relates to a mold releasable composite material that is used during the production of a polyurethane resin synthetic leather in a wet process.
2. Description of the Conventional Art
A synthetic leather is a terminology against a natural leather and generally refers to one comprising a substrate as a backing member, such as non-woven fabrics, woven fabrics, knitted fabrics or sheets, having a polyurethane resin layer, from which a solvent in a resin solution has been removed, lined thereon. Its production process is classified into a dry process and a wet process.
The dry process is a process in which the removal of a solvent in a polyurethane resin solution is effected upon evaporation by heat, thereby producing a polyurethane resin synthetic leather. On the other hand, the wet process is a process in which a solvent in a polyurethane resin solution is extracted in water and dried, thereby producing a synthetic leather. In the dry process, in general, a polyurethane resin solution is applied onto a processing paper comprising a base paper having a mold releasable resin layer provided thereon, at the side of the releasable resin layer and dried by heat to complete a polyurethane resin coating layer; a substrate such as fabrics is joined onto the polyurethane resin coating layer via an applied polyurethane adhesive by means of contact bonding by rollers, etc.; and then, the processing paper is peeled apart to produce a polyurethane resin synthetic leather.
In the wet process, usually, a polyurethane resin solution is applied directly onto a substrate such as fabrics; the applied substrate is introduced into a solidifying tank to extract the solvent, and then washed with water and dried to form a solidified layer (wet process silver layer) of the polyurethane resin, which is rich in fine pores; and if desired, a post treatment is carried out to produce a polyurethane resin synthetic leather.
According to this wet process, in general, innumerable fine pores, from which the solvent has been removed by water extraction, are formed, and hence, the polyurethane resin coating layer becomes in a sponge-like state. Thus, the wet process has an advantage that, though the resulting polyurethane resin coating layer is thicker than that obtained by the dry process, a synthetic leather having a good breathability and a soft feeling is obtained. However, in the case where the substrate such as fabrics is made of a soft material such as tricot, since the substrate has wrinkles or is rich in stretchability, there are defects that it is very difficult to uniformly apply the polyurethane resin solution directly onto the substrate and that deformation occurs depending on the type of the substrate because it passes through water. Thus, it was impossible to produce a thin synthetic leather using a soft substrate.
In order to solve this problem, Japanese Patent No. 2,926,391 disclosed a process in which a polyurethane resin solution is applied onto a release-processed base, a wet process silver layer is formed in the usual wet process, the base is peeled apart to produce a wet process silver layer product, and a substrate is then joined onto the surface, where the base has been peeled apart, of the wet process silver layer product.
Specifically, this process is a process in which a base is subjected to release processing with a silicone-based or fluorocarbon-based water repellent; the release-processed base is applied with a polyurethane resin solution and made pass through a solidifying tank and a water washing tank to solidify the polyurethane resin solution, thereby forming a wet process silver layer; the base is peeled apart to produce a wet process silver layer product; and an adhesive is applied onto the surface, where the base has been peeled apart, of the wet process silver layer product, or an adhesive is applied onto a substrate such as fabrics, and after semidrying, the substrate is joined onto the wet process silver layer product, followed by post treatment such as embossing, printing and/or lamination, to produce a polyurethane resin synthetic leather. According to this process, since it is possible to produce the wet process silver layer product before joining the substrate by using a release-processed base having a strength to a certain extent, it has become possible to produce not only a thin product by joining a soft substrate such as tricot but also a product by joining even a substrate such as a split leather, which becomes unshaped upon being made pass through water, to the wet process silver layer product.
However, according to this process, since a part of the silicone-based or fluorocarbon-based water repellent used for subjecting the base to release processing is transferred to the surface, where the base has been peeled apart, of the wet process silver layer product, there was involved a defect that it is not possible to undergo successfully printing or lamination, or joining of the substrate such as fabrics, on the surface, where the base has been peeled apart, of the wet process silver layer product.
An object of the invention is to provide a mold releasable composite material to be used in producing a polyurethane resin synthetic leather in a wet process, that is capable of overcoming these defects of the conventional art processes, to which a soft substrate such as tricot can be joined, and which is free from any adverse influence in the case where a post treatment such as printing and/or lamination is carried out, or in the case where joining of a substrate such as fabrics is carried out.
The present inventor made extensive and intensive investigations in order to achieve such an object. As a result, it has been found that the object can be achieved by a mold releasable composite material for wet production of a synthetic leather comprising a polymer base and a composition layer laminated on at least one surface of the polymer base, the composition layer consisting of 50 to 95% by weight of a styrenic polymer having a syndiotactic structure and 5 to 50% by weight of a polyolefin, and the mold releasable composite material having a peeling strength of 300 g/15 mm or more.
In addition, the inventor has found that it is preferred that the composition layer consisting of a styrenic polymer having a syndiotactic structure and a polyolefin is subjected to embossing processing; that as the polymer base on which the composition layer consisting of a styrenic polymer having a syndiotactic structure and a polyolefin is laminated, a sheet, a woven fabric, a non-woven fabric, or a knitted fabric comprising at least one member selected from the group consisting of a polyester, polyethylene, polypropylene, a nylon, and an acrylic resin, each of which is a waterproof resin, is used; that the composition layer consisting of a styrenic polymer having a syndiotactic structure and a polyolefin has a crystallinity of less than 30% and a wetting index of 26 to 38; and that an anchor coating agent is used in laminating the above-described composition layer on the polymer base.